Dataset before extension:
 [   0  -1  -2  -3  -4  -5  -6]
 [   0   0   0   0   0   0   0]
 [   0   1   2   3   4   5   6]
 [   0   2   4   6   8  10  12]

Filter type is: H5Z_FILTER_DEFLATE
Dataset after extension:
 [   0  -1  -2  -3  -4  -5  -6   7   8   9]
 [   0   0   0   0   0   0   0   7   8   9]
 [   0   1   2   3   4   5   6   7   8   9]
 [   0   2   4   6   8  10  12   7   8   9]
 [   0   1   2   3   4   5   6   7   8   9]
 [   0   1   2   3   4   5   6   7   8   9]
